Which river is the largest southern tributary of the Ganga in Bihar?

the Ganga flowing through Bihar. The key to this question is the precise association expressed in its wording: “Which river is the largest southern tributary of the Ganga in Bihar?” The answer Son matches that clue directly and is therefore factually appropriate. Option B — Punpun — is incorrect because it does not match the exact person, district, location, institution, river, event or identifying feature required by the question. It may be associated with another Bihar-related context, but that broader association does not satisfy this specific wording. Option C — Falgu — is incorrect because it does not match the exact person, district, location, institution, river, event or identifying feature required by the question. Option D — Kiul — is incorrect because it does not match the exact person, district, location, institution, river, event or identifying feature required by the question. Bihar GK questions frequently place neighbouring districts, related historical personalities, nearby rivers or institutions from the same field among the options. The Son River is the largest southern tributary of the Ganga flowing through Bihar.